Microsoft has offered another small concession to critics of its upcoming products, this time altering plans for its Passport authentication service.

The technical changes come as pressure mounts in Washington to bring a speedy conclusion to Microsoft's ongoing legal battle with the US government.

Microsoft said it will make some changes to the information users are required to provide it when signing up for its Passport service, which is designed to let users visit multiple sites on the web without needing to enter the same personal information each time. Passport is a key element of Microsoft's internet strategy known as .Net.

Passport is used by many of Microsoft's web 'properties', such as its webmail service Hotmail, as well as by a growing list of partners including and The Passport authentication service stores as many as 13 items of basic user information — ranging from postcodes to street addresses — and also includes an 'electronic wallet' component that stores information for making online purchases, such as a billing address and credit card number.

If you've never heard of Passport, this hasn't stopped you from using it — whenever you log into Hotmail or MSN you log into Passport.

Criticism of Passport has mounted from some privacy advocacy groups, who last month filed a complaint with the US Federal Trade Commission (FTC) over concerns about how the service collects data from users and how that personal information might be used in future. Hoping to ease some of that opposition, Microsoft said it will now require a user to enter only an email address and password to open a new Passport account.